1. Field of the Invention
This invention is related to a device for preventing propulsive ignition of a rocket motor exposed to a heated ambient or slow cook-off environment. In particular, the invention is related to a mechanism for sensing the heated ambient and triggering a linear shaped charge to create a stress riser on a motor casing or a pressure vessel. Should the motor subsequently ignite, it vents through the stress riser.
2. Description of the Prior Art
One of the primary dangers from storing pressurized vessels and rockets or missiles arises not from the explosive charge or warhead which may be the missile payload, but rather the rocket propellant or rocket motor itself. In particular, fires and other sources of high ambient heat in proximity to rocket motors or pressure vessels create a high risk that the motors will prematurely ignite or that the vessels will violently release pressure. Dolan, Thermally Activated Rocket Motor Safety System, U.S. Pat. No. 4,597,261, taught a thermally activated safety system for protecting against temperature produced by a fortuitous fuel fire, i.e., fast cook off environment. Fast cook off triggers react to instantaneous, or near instantaneous exposure to high temperature, such as flame. For example, one fast cook off trigger in Dolan, 4,597,621, was designed to activate within 30 seconds when exposed to temperatures above 550.degree. F. to 600.degree. F. Generally, these triggers are not designed to be resettable.
Even though the rocket may not be directly exposed to open flame, there is nevertheless a substantial danger that the rocket motor will be ignited when it is exposed to high ambient temperatures over a prolonged period of time, for example, where the temperature of the rocket motor or pressure vessel itself gradually reaches a predetermined ignition temperature, such as temperatures in excess of 350 degrees F. Instances of such ambient exposure could readily occur when stockpiles of rockets or rocket motors are exposed to ambient heat or convection heat caused by the presence of flame in the ambient environment. Specifically, such an event may occur when a magazine, which may not be directly subjected to fire, is gradually heated due to a fire in a nearby compartment on board a ship (i.e., slow cook off).
In such a case, if one of the rocket motors should ignite from prolonged exposure to heat, not only does it become a destructive ballistic even if unarmed, in many cases the rocket ignition may trigger events causing the warhead to be armed.
Therefore, what is needed is some type of device which is rugged and reliable as to be suitable for use with rocket motors or pressure vessels in a slow cook off environment and yet which is capable of sensing a high ambient temperature and thereby taking responsive action to disable a rocket motor from propulsive ignition, or a pressure vessel from premature explosion.